A Plasma Display Panel (PDP) utilizes a matrix array of discharge cells, which could only be “ON”, or “OFF”. Also unlike a CRT or LCD in which gray levels are expressed by analog control of the light emission, a PDP controls the gray level by modulating the number of light pulses per frame. This time-modulation will be integrated by the eye over a period corresponding to the eye time response.
For stationary pictures, this time-modulation repeats itself, with a base frequency equal to the frame frequency of the displayed video norm. As known from CRTs, a light emission with base frequency of 50 Hz, introduces large area flicker, which can be eliminated by the 100 Hz Upconversion technology for CRT TV receivers.
On the one hand this large area flicker artifact is reduced on a PDP since the duty cycle of light emission is longer. On the other hand since PDPs offer a larger size, even a reduced large area flicker becomes objectionable in terms of picture quality.
The solution, which is implemented in the European 100 Hz Upconversion TV technology, is to display twice as many frames/fields (by repeating each frame/field or by interpolating extra-frames/fields) in the same time period (20 ms), which corresponds to displaying a 100 Hz video. For clarification the term “frame” in TV technology means a complete video picture. The standard TV systems NTSC, PAL, SECAM use the interlace scanning so that a frame consists of two “fields” wherein the first field all odd video lines are displayed and in the second field all the even video lines are displayed. In the 50 Hz TV systems like PAL and SECAM a complete video picture is transmitted in a 40 ms time raster corresponding to a 25 Hz frame repetition rate. The fields are transmitted in 20 ms time raster corresponding to 50 Hz field repetition rate. The 100 Hz Upconversion technology mostly tackles the problem of large area flickering, but usually only by a pseudo frame/field repetition. This solution, as it is, is not really conceivable on the PDP since to display twice as many frames per second, twice as many sub-fields would be required (for the same quality).
Plasma displays are operated in progressive scanning mode in order to avoid a strong line flickering. From another European Patent Application of the applicant (EP-A-0 982 708) a solution is known how to create a pseudo-100 Hz component on the PDP, but this cannot be used to display the video frames coming from a video source reproducing video frames with a rate equal or higher than 75 Hz.
The same limitation occurs when handling high frequency video signals coming from PC applications. In this case PDPs usually drop some frames and display a video at 60 Hz, losing the advantages of the original high frequency video, and introducing some motion artifacts since some frames are constantly dropped.